Effects Of Bovine Leukemia Virus Infection Research Articles

Effect of BLV Infection on the Immune Function of Polymorphonuclear Neutrophil in Dairy Cows.

Enzootic bovine leukemia is a late-onset, neoplastic infection caused by the bovine leukemia virus (BLV). BLV infection hinders the function of the immune system and induces other diseases, which negatively affects the performance and health of the infected cows. As the first line of defense against invading foreign pathogenic microorganisms, polymorphonuclear neutrophil (PMN) plays a vital role in the immune system of dairy cows. However, research on the effect of BLV infection on the immune function of PMN in dairy cows is scarce. Therefore, this experiment aimed to elucidate the effects and effect mechanisms of BLV infection on the immune function of PMN in dairy cows with different BLV provirus loads by detecting the chemotaxis, migration, adhesion, phagocytosis, respiratory burst function, and the formation of NETs. The experimental results showed that BLV infection had no significant effect on the phagocytosis of PMN but inhibited their migration and respiratory burst function, and the effects were closely related to the BLV provirus load. Under high BLV provirus load, PMN produced large amounts of NETs, chemokine CXCL7, adhesion molecule CD18, and pro-inflammatory factors IL-8 and TNF-α, triggering inflammatory responses, and tissue damage. The results of this study will help reveal the reason why BLV infection causes the high incidence of mammary gland inflammation in dairy cows.

Milk Macrophage Function in Bovine Leukemia Virus-Infected Dairy Cows.

The implications of bovine leukemia virus (BLV) on innate and adaptive immune responses have been widely investigated; however, the effects of BLV on mammary gland immunity require further investigation. The present study investigated the viability, phagocytic capacity, and intracellular production of reactive oxygen and nitrogen species (RONS) by macrophages in milk samples from dairy cows naturally infected with BLV with or without persistent lymphocytosis (PL). No effect of BLV infection in the overall number of macrophages per milliliter and in the percentage of viable macrophages among overall milk viable cells was found. Furthermore, BLV-infected dairy cows had a higher frequency of viable milk macrophages, while healthy animals had a tendency toward a higher percentage of apoptotic milk macrophages. The percentage of milk macrophages that phagocytosed Staphylococcus aureus in seronegative animals was higher than that in BLV-infected dairy cows. No effect of BLV infection on the intracellular RONS production and the intensity of phagocytosis by milk macrophages was observed. Thus, this study provides new insights into the implications of BLV infections in the bovine mammary gland.

Bovine Leukemia Virus Alters Growth Properties and Casein Synthesis in Mammary Epithelial Cells

Bovine leukemia virus (BLV) is widespread in US dairy herds, yet only about 1% of infected cattle develop bovine leukosis and are culled from the herd. A major concern is whether BLV infection of dairy cows alters milk yield. Although several studies have examined the effect of BLV on milk production in vivo, the results were inconclusive. No in vitro studies have been done. The discovery of BLV in mammary epithelial cells (MEC) of infected cows raises the possibility that the virus could affect these cells directly. The purpose of this study was to use an in vitro system to determine if BLV could alter milk yield by altering cell number and/or milk production per cell. A short-term cell line established from the MEC of a BLV-negative cow, and a proven casein-producer mouse cell line, Comma D, were stably transfected with a plasmid containing the entire BLV genome. Untransfected parental lines served as negative controls. The BLV-containing bovine MEC line has a reduced population-doubling time, higher saturation density, and increased longevity. The Comma D line is an already-transformed cell line, and growth properties did not change after transfection with BLV. Under appropriate differentiation conditions, both the bovine and mouse MEC transfected with BLV displayed decreased casein production and mRNA synthesis compared with control cell lines without BLV. Our results suggest that effects of BLV infection on milk production may not be related solely to overall animal health but may also be mediated directly at a cellular level.

Lymphocyte colony formation by aleukemic sheep infected with bovine leukemia virus

The objective of this study was to investigate the effects of bovine leukemia virus (BLV) infection in sheep. A prospective study of the serologic, hematologic, and histologic changes of sheep infected with BLV was conducted. Antibodies to BLV were detectable in the sheep 3 weeks after exposure to blood from an infected cow and persisted during a 120 week examination period, whereas all control sheep remained seronegative. There were no statistically significant differences between the leucocyte counts, lymphocyte counts, and lymphocyte percentages of the infected and control sheep during the first 120 weeks of this study. However, one sheep did develop a leukopenia and lymphopenia 95 weeks after it became infected and died of histologically-confirmed lymphosarcoma 10 days later. A lymphocyte colony assay was used to study the effects of BLV infection on colony formation by sheep lymphocytes in vitro. There was no significant difference in the number of lymphocyte colonies formed by BLV infected and control sheep. Nor was there a significant difference in the number of colonies formed by lymphocytes from the BLV infected sheep, when the autologous sheep serum was replaced with either pooled serum from the infected sheep or with pooled serum from the control sheep. BLV infection in aleukemic sheep does not appear to have an adverse affect on colony formation by lymphocytes in vitro.

Relationships between herd bovine leukemia virus infection status and reproduction, disease incidence, and productivity in Swedish dairy herds

A program has been initiated in Sweden to eradicate bovine leukemia virus (BLV) infections in dairy and beef cattle. As the first step, all dairy herds were screened in order to identify those with BLV-infected animals. The objective of this study was to ascertain possible relationships between herd BLV infection status and measures describing disease incidence, reproduction and production. BLV infection status was determined in 14 424 herds, using an enzyme-linked immunosorbent assay (ELISA) test applied to bulk-milk samples. Relationships were assessed with logistic and ordinary linear regression analyses. There were many statistically significant associations between herd BLV infection status and measures of disease incidence, reproduction and production, but most were of low magnitude. The risk for diseases with infectious etiology seemed to be greater among BLV-infected herds, while the risk for non-infectious diseases did not differ. The culling rate was higher and milk production was lower in BLV-infected vs. BLV-free herds. The effect of BLV infection on fertility was only minor.